The United States said it was in talks with Ivory Coast's neighbours about mustering UN reinforcements, and the World Bank said it had agreed with these West African capitals to halt loans to the regime.
The new pressure on Gbagbo came after UN Secretary General Ban Ki-moon warned Ivory Coast faces "a real risk of a return to civil war" unless Gbagbo stands down and hands power to his rival Alassane Ouattara.
Supporters of Alassane Ouattara, who has claimed to have won last month's presidential election, burn tires in a street in Abidjan on December 16. Supporters of would-be Ivory Coast president Ouattara urged world powers Wednesday to use military force to oust defiant strongman Laurent Gbagbo.
World Bank president Robert Zoellick said in Paris that he had agreed with the leaders of Ivory Coast's partners in the West African Economic and Monetary union that Abidjan be cut off from international funding.
"They are also convening a meeting of ministers this week to affirm and strengthen this approach," he said of the West Africans, after holding talks with France's President Nicolas Sarkozy.
"We are in discussions with other regional countries to see if there are ways in which we can reinforce the UN peacekeeping force," State Department spokesman Philip Crowley said in Washington.
Crowley said Washington was in talks with the Economic Community of West African States (ECOWAS), and a diplomat in Abidjan confirmed a "military option" would be at the table at the bloc's crisis summit on Friday.
Ouattara's camp has welcomed international support, but his would-be prime minister, former rebel leader Guillaume Soro, had a stark message.
"After all the international pressure and the sanctions which did not have any effect on Mr Gbagbo, it's obvious that only one solution remains, that of force," Soro told France's i-Tele.
"I call on the United Nations Security Council, the European Union, the African Union and ECOWAS to envisage using force," he declared.
Every day now brings new international action against Gbagbo. On Wednesday, the European Union confirmed that visa bans had gone into effect against him and 18 close associates.
"The EU recalls that the result of the presidential election, in favour of President Alassane Ouattara, can neither be submitted to any form of evaluation nor be questioned," top EU diplomat Catherine Ashton said.
"On the contrary, it is important that transfer of power takes place without delay and without preconditions," she added.
The new measures reflect rising frustration at Gbagbo's refusal to step down in favour of his rival Ouattara, who also claims to have won last month's election and has been recognised as president by world powers.
The streets of Abidjan were lively, with traffic jams signalling the return to work for many after a month of crisis, but tensions remain high and former colonial power France urged its nationals to leave.
Many of the estimated 15,000 French expatriates have left for Christmas or to escape the mood of fear. Those who have not left should now depart "provisionally", French government spokesman Francois Baroin said.
Several other countries, including the United States, had already advised citizens to leave, and Nigeria said it was bringing out diplomats' families after a security incident at its embassy.
Gbagbo has deployed his armed forces to put down pro-Ouattara protests and to bottle up his adversary in the Golf Hotel, a luxury Abidjan resort protected by 800 UN peacekeeping troops.
"I am president of Ivory Coast. I thank the Ivorians who renewed their faith in me," Gbagbo declared late Tuesday, in a rare televised address.
The 65-year-old strongman accused the United Nations of "making war" on his people, and insisted French and UN peacekeepers would have to leave.
United Nations human rights and peacekeeping officials have accused Gbagbo's security forces of "massive human rights abuses" and are probing reports that he has hired Liberian mercenaries as death squads.
On Tuesday, Ban issued a plea on behalf of the troops in the United Nations 9,000-strong UNOCI peacekeeping mission, in particular those dug in around the Golf Hotel in Abidjan protecting Ouattara's besieged shadow government.
He warned the UN General Assembly that a "disruption of life-support supplies for the mission and the Golf Hotel will put our peacekeepers in a critical situation in the coming days."